Hundreds of people have marched in South Korea’s capital demanding Japan scrap its plans to release treated wastewater from the damaged Fukushima nuclear power plant.

The protests came a day after South Korea’s government formally endorsed the safety of the Japanese plans, saying that the contamination levels of water pumped out from the plant would be within acceptable standards.

The announcement aligned with the views of the International Atomic Energy Agency (IAEA), which approved the Japanese discharge plans this week, saying the treated wastewater would meet international safety standards and pose negligible environmental and health impacts.

Braving blistering summer heat and closely watched by police, the protesters walked in long lines through a commercial district in downtown Seoul, holding signs reading “We denounce the sea disposal of Fukushima’s nuclear wastewater!” and “We oppose with our lives the sea discharge”.

“Other than discharging the water into the sea, there is an option to store the water on their land, and there are other options being suggested,” said Han Sang-jin, spokesperson of the Korean Confederation of Trade Unions, whose members accounted for many of the marchers.

He said that allowing Japan to discharge the water “is like an international crime”.

The protests provided a tense backdrop to a meeting between IAEA director General Rafael Mariano Grossi and South Korean foreign minister Park Jin, which was expected to include discussions over people’s fear of food contamination.

Speaking to reporters in Tokyo on Friday before his flight to South Korea, Mr Grossi said he was aware of the unease in South Korea and was willing to communicate more actively with critics, including South Korean opposition politicians, to reduce concerns.

Hours later, he was greeted by dozens of angry protesters at an airport near Seoul.

They denounced the IAEA’s support of the discharge plans, holding signs reading “Dismantle IAEA!” and “Fukushima wastewater will definitely lead all humanity to disaster!”

Mr Grossi is also expected to meet lawmakers from the opposition Democratic Party, which has harshly criticized the Japanese discharge plans and accused the conservative government of South Korean president Yoon Suk Yeol of putting the nation’s health at risk while desperately trying to improve relations with Tokyo.

The safety of Fukushima’s wastewater has been a sensitive issue for years between the US allies. South Korea and Japan have been working in recent months to repair relations long strained over wartime historical grievances to address shared concerns such as the North Korean nuclear threat and China’s assertive foreign policy.

South Korea’s assessment about the safety of the discharge plan was partially based on observations by a team of government scientists who were allowed to tour the Fukushima plant in May.